1. Field of the Invention
The present invention relates generally to a wireless local network (WLAN) communication, and, more particularly, to a technique for increasing the speed of WLAN communication.
2. Description of the Related Art
WLAN communication is wireless communication technology based on the IEEE 802.11 standard. Although not supporting mobility, the WLAN communication is widely employed in notebook, smart phone, portable storage device, camera, etc. because the WLAN can efficiently expand a network area wirelessly at a terminal tip of an LAN.
As the number of WLAN-supported devices used in daily life becomes increasingly larger, various problems occur in terms of transfer rate or wireless quality management.
For example, the IEEE 802.11 standard allows wireless communication apparatuses to operate at various transfer rates. Nevertheless, since the equal opportunity to access a channel is provided to all nodes, the performance of high speed transmission nodes that access a corresponding WLAN may be considerably deteriorated if a plurality of devices of relatively low transfer rates accesses the WLAN. This phenomenon is often referred to as performance anomaly.
In order to overcome this problem, time fairness approach that assigns proper transmission time slots to respective nodes, taking into account the size of data, that is, the length of a transmission queue, that should be transmitted by each of the nodes has been proposed.
Furthermore, IEEE 802.11 allows for a plurality of frequency channels. As an increasingly large number of access points and nodes occupy the same space, frequency collision may occur between access points using the same frequency channel. Since a WLAN technology is designed such that a transmitting node should receive an acknowledgement signal indicative of the proper reception of data from a receiving node after transmitting a packet and then transmit the next packet, data transfer rate may be significantly reduced if data is not normally transmitted and received due to frequency collisions.
Meanwhile, a cooperative transmission technique is a communication technique in which a low speed node selects a high speed node as a relay node and allows the relay node to forward its transmission data, thereby overcoming the problem of low transfer rate.
The cooperative transmission technique incurs overhead because a procedure in which a low speed node investigates adjacent nodes, searches for and selects a high speed node that will forward data on behalf of itself, and obtains permission should be undergone. Even a high speed node selected for cooperative transmission cannot overcome the problem of a reduction in transfer rate when a frequency collision occurs, and the improvement of performance cannot be achieved as much as expected if channel access time is not appropriately assigned.